The present invention relates to the field of solid-propellant rocket motors. It relates more particularly to the destruction of reformed rocket motors, especially those that have reached the limit of their operational use and have been removed from service.
A solid-propellant rocket motor essentially comprises a hollow cylindrical casing inside which is placed at least one block of solid propellant—to simplify matters we will refer hereafter to one block of propellant. One end of the casing is closed off by a dome and the opposite end by a nozzle; the dome and the nozzle will be regarded as forming part of the casing.
The rocket motors considered here are those for which the block of solid propellant has been fastened to the casing and cannot be removed simply from the casing. These are essentially what are called “cast-bonded” motors for which the block of propellant, during manufacture of the motor, is cast in and bonded to the casing suitably prepared for this purpose. We shall liken to this type of motor those for which the block of propellant, prepared elsewhere, is introduced and fitted irreversibly into the casing, this fitting operation being intentional or accidental. We shall retain the expression “cast-bonded” rocket motors to denote the motors treated in this invention.
The destruction of a rocket motor consists firstly in placing it in a state such that it cannot fulfil its propulsion function and then secondly in separating the casing from the propellant in order to treat them separately, taking into account the fact that only the propellant involves a pyrotechnic risk, which requires special precautions and conditions in its treatment for the purpose of scrapping or recycling certain components.
The problem more particularly tackled here is that of how to destroy a very large number, typically several thousand, of rocket motors; it is necessary to be able to treat several tens of motors per day.
Both the destruction process and the destruction plant must be capable of operating at a very high rate. What is therefore required is a process with simple and rapid steps and an unsophisticated plant.
In addition, the process and the plant must be reliable. An incident occurring on a motor or part of a motor during one step of the process must remain limited, or be able to be limited, to this part of the motor, and to the location in the plant where the said incident occurs. The incident must not propagate throughout the plant and become catastrophic, owing to the large number of motors necessarily present on the destruction site.
The prior art discloses several processes for destroying rocket motors, but under conditions which do not correspond to the problem posed, as we will see during the course of analysing these processes.
U.S. Pat. No. 5,220,107 discloses the fragmentation of a block of bare propellant, that is to say one not bonded to the inside of the casing of a rocket motor, by cooling the block of propellant down to a very low temperature and by using a crusher or a press to fragment it.
U.S. Pat. No. 5,025,632 discloses the extraction of the propellant from a cast-bonded rocket motor with a central channel using at least one jet of cryogenic liquid. This destruction process, derived from a “water knife”, is very lengthy and does not meet the requirement for a high work rate. In addition, it is potentially hazardous as the work is carried out on an entire rocket engine.
U.S. Pat. No. 5,552,093 discloses the extraction of the propellant from a cast-bonded rocket motor that has been cooled by immersion in liquid nitrogen. The block of propellant is fragmented, especially by applying mechanical shocks to it. The application of shocks to the propellant, even when cooled, is still potentially hazardous, and this hazard is greater owing to the fact that, here again, the work is carried out on an entire motor. In addition, for relatively long motors, the possibility of fragments becoming jammed in the casing, and requiring further handling operations to extract them from the casing, cannot be ruled out.